tests: Format all Python code with black, except tests in basics subdir.

This adds the Python files in the tests/ directory to be formatted with
./tools/codeformat.py.  The basics/ subdirectory is excluded for now so we
aren't changing too much at once.

In a few places `# fmt: off`/`# fmt: on` was used where the code had
special formatting for readability or where the test was actually testing
the specific formatting.

tests/cpydiff/core_locals.py

@@ -4,8 +4,11 @@ description: Local variables aren't included in locals() result
 cause: MicroPython doesn't maintain symbolic local environment, it is optimized to an array of slots. Thus, local variables can't be accessed by a name.
 workaround: Unknown
 """
+
+
 def test():
     val = 2
     print(locals())
 
+
 test()